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Biomechanics of Soft-Tissue Interference Screw Fixation for Anterior Cruciate Ligament Reconstruction
Abstract & Commentary
Synopsis: When using bioabsorbable interference fixation with a soft-tissue ACL graft, increase the graft stiffness by reaming the tunnels smaller than the graft, dilating the tunnel to no more than 0.5 mm greater than the graft, and choosing a screw length and diameter that is maximal for the tunnel created. Interference fixation of a soft-tissue graft also depends upon the quality of the patient’s tibial and femoral bone.
Source: Brand JC Jr, et al. Biomechanics of soft-tissue interference screw fixation for anterior cruciate ligament reconstruction. Orthopedics. 2003;26(4):432-439.
This article reviews interference fixation methods for soft-tissue grafts used for cruciate ligament reconstruction. As explained by Brand and associates, quadriceps and quadruple hamstring tendon grafts are becoming more popular as choices for ACL and PCL reconstructions, as they avoid the complication of not only anterior knee pain but also late patella baja.
In the past, soft-tissue grafts were fixed at the tunnel origin with staples, screws, and posts and various suspension fixation methods. In 1997, Pinczewski and colleagues1 described fixation of a quadruple hamstring graft with a titanium metal interference screw. Shortly thereafter, Fu2 reported use of a biodegradable interference screw for the same purpose, and Brand and associates3 described the use of this fixation device for a quadriceps tendon ACL graft. Such interference fixation improves the fixation stiffness above that of a post and washer or closed-loop endobutton fixation. According to Brand et al, interference fixation of a soft-tissue graft results in direct-contact healing of the graft to bone instead of formation of a fibrous interface as seen with extraarticular fixation (post and screw, endobutton, staple, etc). Interference screw fixation for soft-tissue grafts has poor failure loads, especially with cyclical loading.
To improve load to failure for biodegradable interference fixation of soft-tissue grafts, Brand et al’s suggestions include using this type of fixation only when there is good quality bone, sizing the graft to within 0.5 mm of the bone tunnel and drilling smaller tunnels, dilating to the appropriate size, and using screws of maximal length and diameter for the tunnel created.
Comment by Letha Y. Griffin, MD, PhD
Recent reports of patella chondromalacia secondary to patella baja following harvest of patella tendon grafts, added to the previously reported improved cosmesis for hamstring graft harvest, have heightened the interest in hamstring grafts for ACL reconstructions. However, in the last several years, various authors have reported on the poor stiffness and greater failure of interference fixation of soft-tissue grafts, especially with repetitive loading as seen with more aggressive rehabilitation programs. Brand et al provide suggestions to improve this
fixation. Altering rehabilitation programs during the initial 3-6 postoperative weeks should also be considered. For example, avoid active quadriceps loading of the knee from 0° to 45° and consider partial weight bearing for the first several weeks postoperatively.
Dr. Griffin is Adjunct and Clinical Faculty, Department of Kinesiology and Health, Georgia State University, Atlanta, GA.
1. Pinczewski LA, et al. Arthroscopy. 1997;13:661-665.
2. Fu F. Orthopaedics Today. 1997;16:36-37.
3. Brand J Jr, et al. Arthroscopy. 2000;16:805-812.